Need help with p0420
02-05-2019, 02:57 PM
#1
Thread Starter
Join Date: 02-05-2019
Location: Texas
Posts: 5
Need help with p0420
I have a 2011 hhr I have replaced the cat both o2 sensors twice I reset the code it comes back a few day later and when it comes back on feels like car is sluggish then it will go back to normal any one have any other clues I order a set of injectors thinking it might be one bad injector ?? Any help would be appreciated this car only has 85k miles ran amazing then had this issue and local Chevy dealer ripped me off $800 for a new intake boot and air duct and also throttle body wireing harness still have same issues. And I had a loose ground wire I found on the fender and all other codes went away but the p0420 code keeps popping up.
New parts : cat, both 02 twice replaced ,new sparkplugs and coils, injectors not installed yet
New parts : cat, both 02 twice replaced ,new sparkplugs and coils, injectors not installed yet
Last edited by Ark4utx3; 02-05-2019 at 03:00 PM. Reason: Information forgot
02-05-2019, 03:41 PM
#2
Administrator
Join Date: 10-13-2011
Location: Welland,Ont Canada
Posts: 36,493
Welcome to the site, thanks for the explanation and the list of replaced parts.
https://www.obd-codes.com/p0420
As as we see here , the wire harness connections need to be checked, a burnt wire or loose pins in the o2 sensors connections.
you also need to inspect for exhaust leaks , yes you have a new catalytic converter , but are the gaskets at the flange and exhaust manifold ok?
injectors I doubt will help, but they are easy enough to replace.
Are you looking at it or are you going back to the same place and instruct them what to look for?
I suggest a new mechanic with some good old shade tree , hot rodding back ground.
your guys , not so much!
https://www.obd-codes.com/p0420
As as we see here , the wire harness connections need to be checked, a burnt wire or loose pins in the o2 sensors connections.
you also need to inspect for exhaust leaks , yes you have a new catalytic converter , but are the gaskets at the flange and exhaust manifold ok?
injectors I doubt will help, but they are easy enough to replace.
Are you looking at it or are you going back to the same place and instruct them what to look for?
I suggest a new mechanic with some good old shade tree , hot rodding back ground.
your guys , not so much!
02-05-2019, 04:16 PM
#3
Technical Moderator
Join Date: 01-23-2009
Location: Fredericksburg, Virginia
Posts: 24,683
I had the same problem on my 2011. I never solved it. Changing the injectors fixed it for a week. The P0420 test is the last test to run after the EVAP tests which can take 20 cold start cycles (in my case 2 weeks) that's why it seems to be fixed for a week or so. If you need a smog test reset the codes and get to the test station 2 days later to get most of the tests in ready mode. Most states let you get away with 1 or 2 "not ready".
Mine always ran fine even when the CEL was on. Yours could be the injectors, that was the best result for me. You will need the new cups and seals when you do them.
There is a chance that a firmware refresh for the ECM will do the job, I never got that far.
I replaced:
O2 sensors
cat/downpipe
exhaust gasket
TB gasket
O2 sensor spacer (both)
Mine always ran fine even when the CEL was on. Yours could be the injectors, that was the best result for me. You will need the new cups and seals when you do them.
There is a chance that a firmware refresh for the ECM will do the job, I never got that far.
I replaced:
O2 sensors
cat/downpipe
exhaust gasket
TB gasket
O2 sensor spacer (both)
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